Urgent help needed - Steelcase or Knoll?  

No Knoll
You are about to buy a Steelcase group.

D'oh!
Double post.

Positive? If so - could you...
Positive? If so - could you please elaborate on how you come to this conclusion?
They claim they're in possesion of a 1965 receipt from Knoll International - I have yet to see it though.
I am obviously extremely grateful for any input on this matter - Thank you!

I thought they were Knoll - I...
I thought they were Knoll - I have a Steelcase. Steelcase tufted cushions normally have 5 square rows, not four. The proportions seems lower, sleeker too than mine ...But I think Pegboard is much more of an expert than me.

Details
It's all in the details.
The Florence Knoll design that is a copy of does not have loose cushions, the proportion of the body between the seat cushion and the base is thiner, and the base should be segmented, not cut and welded at an angle.
Regardless, it's still a handsome set and the quality of vintage Steelcase can often exceed that of Knoll when it comes to the framing and internal construction. If you like the look and it's priced right, I say buy it.

Confused
Thank you for your answers!
I am still a little confused though - the Auction House, who are well respected in Europe and have a very strict policy regarding authenticity are still claiming this is a genuine Knoll intl. item and that they have a Knoll receipt for the item from 1965.
The also say the cushions ARE fixed. Should both the bottom and back cushions be fixed on this model?
Thanks again...

Yes
Both the seat and back cushions should be fixed, not loose. They sure look like loose cushions in the photos, but maybe that is just the reupholstery job. Looks like the seat cushion is a tad thick also. The proportions are very close, and I SUPPOSE that the base could have been made differently at some point, stranger things have happened and they do job out components to different vendors, but every one I've ever seen had a segmented base with the seams running vertically. It has to do with how the base is constructed. The legs bolt to the horizontal member.
The sofa is model 65 and measures 90"wide, 31.5" high and 30" deep. The chairs are model 65A and should be 34" wide with the same height and depth. The design was produced between 1958 and 1973.
It would be interesting to see the receipt.

My Steelcase has fixed cushio...
My Steelcase has fixed cushions on the back and loose cushions on the seat.
My Steelcase sofa also has segmented base much like a Knoll.
And there are KNoll sofas with angled legs on the back, which makes it even more confusing. I have a pal with a gorgeous leather knoll armless sofa ... angled legs with tags.
Seems Steelcase and Knoll share many characteristics. Many of the differentiating factors you've listed, Pegboard, I have seen on both brands believe it or not.
That being said, I LOVE my Steelcase. Built like a tank, beautiful, and not worth so much that I am afraid to use it regularly.

Again - so many thanks for yo...
Again - so many thanks for your valuable input. I will speak to the Auction House by phone tomorrow and hope they can scan or fax me the invoice so I can have a look at it.
I have been scouring the internet for decent photos of the models, just found a few where you can actually tell but those definitively all have the segmented base.. It has been reupholstered which could explain the questions regarding the pillows..
Any ideas on who you would contact if I would need to have a final verdict on this? Would knoll have someone that actually knows anymore?

Knoll customer service
can help you positively ID it. Send an email with the photos.
Sometimes it takes a few days for the response, so I hope the auction isn't too soon.

Thanks, definitively will do...
Thanks, definitively will do that - thing is I've already won the auction but of course wont be obliged to fulfill the deal if it turns out it was wrongly advertised as authentic Knoll.. to be continued.

update?
update?

Not really - waiting for an...
Not really - waiting for an answer from Knoll now.
Talking to the auction house they said two Knoll side tables that were also on auction had been part of the set and that they still had the Knoll labels on them. Also, both seat and back cushions were fixed. Have yet to see the receipt though..

Over two weeks since I...
Over two weeks since I contacted Knoll now.. Neither I nor the auction house, who has also contacted them, has received an answer. Would anyone know who specifically at Knoll you should contact or who would be considered such an expert at Knoll furniture they could make a final judgement?
Thanks again.